The proposal, Japan's latest step away from the constraints of its pacifist constitution, is part of a review of defence policy by Prime Minister Shinzo Abe's government, which released an interim report on the subject on Friday. Final review conclusions are due by the end of the year.

The hawkish Abe took office in December for a rare second term, pledging to bolster the military to cope with what Japan sees as an increasingly threatening security environment including an assertive China and an unpredictable North Korea.

The report by a defence ministry panel echoed concerns aired in Japan's latest defence white paper about North Korea's missile and nuclear programmes, and China's military build-up and increased activity by its ships and aircraft near disputed islands in the East China Sea.

Japanese and Chinese vessels and planes have been playing cat-and-mouse near the islands, called the Senkaku in Japan and the Diaoyu in China.

Given Japan's strained ties with China over the tiny islands and Tokyo's wartime history, Beijing could react strongly to the proposals, which come after Abe cemented his grip on power with a big win in a weekend election for parliament's upper house.

The Defence Ministry panel said that it was necessary to comprehensively strengthen "the ability to deter and respond to ballistic missiles". But in a sign of the sensitivity of the issue, a ministry official denied that this implied Japan would make pre-emptive strikes against enemy bases.

"It is necessary to consider whether we should have the option to strike an enemy's missile launch facilities," the official said. "But we are not at all thinking about initiating attacks on enemy bases when we are not under attack."

The line between the ability to hit enemy targets and make pre-emptive strikes is primarily political and philosophical, and Japanese officials typically avoid the latter term. Acquiring the capability for pre-emptive strikes against enemy missile bases would be difficult and costly, experts said.

"There is no change at all to our basic policy of exclusively defensive security policy," Japanese Defence Minister Itsunori Onodera told reporters.

"The issue of capability to strike enemy targets surfaces as we discuss what kind of defence measures we can take when multiple attacks have been mounted against our country."

In the Japan-US security alliance, Japan acted as a shield while United States shouldered the capability to strike enemy bases, he added, but changing security risks needed study.

"Broad-based debate, including one between Japan and the United States, is needed on the issue amid the changing security environment," Onodera said.